The present invention relates to a facsimile apparatus which can have communication with a remote receiver regardless of the type of the latter and, more particularly, to a system for adding fill bits to compressed data bits in the event the compressed data are to be transmitted from the transmitter to the receiver.
Facsimile transmission systems are extremely useful for transmitting original documents in numerous commercial and bureaucratic applications. The original document is scanned to produce electrical signals which are transmitted over a telephone line or the like to a remote receiver. The receiver prints a facsimile or reproduction of the original document in response to the received signals. In order to increase the transmission speed, it is desirable to compress the signals for transmission using run length encoding or the like.
The original document is scanned to an orthogonal pattern of scan lines and the signals are transmitted on a line by line basis. Each line of compressed data consists of data bits and fill bits. A sync code is added at the end of each line. In order to minimize the buffer memory requirements of the receiver, each line of data has a predetermined length and the printer at the receiver is constructed to print each line faster than it is compressed and transmitted. Thus, each line of compressed data has a predetermined number of bits. Often, the run length code is quite short, and fill bits, generally consisting of zeroes, are added to the data bits to increase the length of the line to the predetermined value. Printing of a new line is effected in response to detection of a sync code.
A problem has existed heretofore in this type of facsimile transmission system regarding insertion of fill bits. Where an actual transmission time for one line of compressed data, that is, an actual length of one line of compressed data is shorter than the predetermined value mentioned above, it has been customary to add fill bits to the data bits line by line so that the one line transmission time or one line bit length increases beyond the predetermined value. With such a known system, video data in a whole page connot be transmitted without accompanying a substantial number of fill bits in total. This only serves to limit the effect of data compression which is laboriously employed to shorten the transmission time. Though the total number of necessary fill bits may be reduced if the data reading or data recording operation is sped up, it is difficult at the present stage of development to increase the reading speed or the recording speed, particularly the latter. Speeding up the reading and recording operations will make the apparatus too expensive as a whole to find a wide range of applications.